1. Field of the Invention
This invention relates to hydrogel polymer coatings for natural rubber and synthetic latex articles and to improved methods of applying such coatings. More specifically, the invention relates to a hydrophilic water soluble polymer in an alcohol-free solution and a method for applying this material to natural rubber latex and synthetic latex articles. The hydrogel coating of the invention makes it easier for the user to don the rubber or latex article bearing the coating.
2. Description of the Related Art
Hydrogel polymers or resins are coated on rubber and synthetic latex products, such as surgical gloves, condoms, catheters, and ureters to enhance the lubricity of the product when in contact with human skin or tissue, i.e., to facilitate donning the rubber or latex product to which the polymer has been applied. For example, in the case of uncoated latex surgical gloves, which have poor lubricity relative to skin, the gloves are difficult to don and require a lubricant to be applied to the inner surface of the glove to facilitate donning of the glove. Prior art lubricants have included powder materials, such as particulate epichlorhydrin-treated maize starch, applied conventionally to the inner surface of the glove to ease donning of the glove. However, powdered lubricants are undesirable in that there is a risk that the lubricant will escape from the interior of the glove and contaminate the surgical field. Also, starch powder has been implicated as a carrier of latex allergens that are responsible for latex allergies that affect health care workers and others.
As a further solution to the problem, polymeric lubricant coatings have been developed which are permanently bonded to the surface of the rubber or latex article. For example, U.S. Pat. No. 3,813,695 discloses a surgeon's glove formed of a flexible material, such as natural rubber or synthetic latex, with an inner (skin contacting) layer consisting of a polymerized hydrogel coating and a silicone liquid for increasing the lubricity of the interior of the glove.
U.S. Pat. Nos. 4,548,844, ('844 patent) also discloses a surgical glove with a coating of a hydrogel polymer on the inner surface of the glove. The polymerized lubricant coating of the '844 patent is hydrophilic, i.e., water absorbing, and is intended to increase the comfort of the surgical glove to the wearer. The hydrogel coating of the '844 patent is applied to the inner surface of the glove prior to heat vulcanization and curing of the polymer. One of the polymers disclosed in the '844 patent consists of 2-hydroxyethyl methacrylate (HEMA) and acrylic acid (AcAc) at a ratio of approximately 90% HEMA to 10% AcAc. The HEMA/AcAc polymer is applied to the surgical glove in an aqueous solution. The ability of a polymer to form a continuous film on a substrate after coating is important to forming a final polymer coating that is durable and of high quality. The HEMA as a copolymer with acrylic acid may achieve water solubility but the high concentration of acrylic acid affects the film properties in a deleterious manner forming a coating which is patchy and has poor consistency.
The '844 patent also discloses a terpolymer of HEMA, methacrylic acid (MAA) and 2-ethylhexyl acrylate (EHA). The terpolymer requires the use of ethanol for maintaining the polymers and monomers in solution. The use of ethanol in a polymer solution is generally undesirable because ethanol is expensive, creates a fire hazard and presents a waste disposal problem. Thus, it would be preferable to formulate a hydrogel polymer that is soluble in an aqueous solution for use in coating latex articles and for other applications.
While the formulation is crucial to the quality and characteristics of a hydrogel polymer coating, the method of applying the polymer to the natural rubber or latex substrate is also important. In prior art methods for the application of a polymeric coating to the surface of a rubber or latex article, the latex or rubber is generally heat dried prior to applying the coating. Additionally, the prior art generally requires an acid priming step to prepare the rubber or latex article for receiving a hydrogel polymer coating. The acid priming step generally involves immersing the rubber or latex article in an acid solution. Following immersion, the article is rinsed to remove any residual acid. Use of an acid priming step in a coating operation has proven to be undesirable because it is an additional step that is time consuming and expensive. Moreover, the acid presents a waste disposal problem and requires that the article to be treated undergo an additional rinse step.
U.S. Patent No. 4,575,476 ('476 patent) discloses a latex surgical glove having bonded to its inner surface a layer of hydrogel polymer consisting of a copolymer of HEMA with MAA or in the alternative a terpolymer of HEMA, MAA and EHA. In fabricating the surgical glove, hand-shaped mandrels are dipped into rubber or latex to produce a thin rubber coating on each mandrel. The coated mandrels are then leached in hot water and the hand-shaped mandrels are primed for coating by dipping the mandrels in dilute sulfuric acid and rinsed to remove the sulfuric acid. The rubber, still on the mandrels, is then dipped into a 4% ethanol solution of a HEMA/MAA/EHA terpolymer, having a monomer ratio of 5:1:2, plus cross-linking agents and curing catalysts. The rubber is then vulcanized and the polymer simultaneously cured.
The '844 patent teaches an acid priming technique similar to the one disclosed in the '476 patent. In the '844 patent, each glove former or mandrel is first dipped in a coagulation solution such as calcium salt and dried. The glove mandrel is then dipped in a conventional solution of latex rubber and heated to dry the latex rubber. The coated mandrel is then dipped in a leach tank of water (70.degree. C.) for several minutes and thereafter immersed in a solution of dilute sulfuric acid and rinsed.
Consequently, there exists a need for a water soluble hydrophilic polymer coating that is also alcohol-free thereby avoiding the problems associated with polymer coatings that employ an organic solvent such as ethanol. The polymer coating should be applicable to the surface of a rubber or latex article in a single step that does not require an acid priming and rinse step prior to application of the coating to the rubber or latex articles.
All patents and references referred to throughout this specification are hereby incorporated by reference.